MyMediaTools

Convert M4B to OGG — Free Online Tool

Convert M4B audiobooks and podcasts to OGG Vorbis format, replacing AAC audio with the open, royalty-free Vorbis codec while preserving chapter markers. This tool runs entirely in your browser using FFmpeg.wasm — your audiobook files never leave your device.

FFmpeg Command

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Estimated output:

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How It Works

M4B files store audio as AAC inside an MPEG-4 container, along with chapter markers, bookmarks, and metadata tags that make them function as structured audiobooks. During conversion, the AAC audio stream is fully decoded and re-encoded as Vorbis inside an OGG container — this is a full transcode, not a remux, because AAC and Vorbis are fundamentally different codecs with no pass-through option. The OGG container does support chapter metadata, so chapter timing data from the M4B can be preserved in the output. However, M4B-specific features like Apple's bookmarking (which tracks your listening position) are not part of the OGG specification and will be dropped. The Vorbis encoder uses variable bitrate (VBR) encoding controlled by a quality scale rather than a fixed bitrate, which is why the -q:a parameter is used instead of a bitrate flag.

What Each Flag Does

Flag What it does
ffmpeg Invokes the FFmpeg multimedia processing tool. In this browser-based tool, FFmpeg runs locally via WebAssembly (FFmpeg.wasm), meaning the same open-source engine is used without sending your audiobook to any server.
-i input.m4b Specifies the input file — an M4B audiobook or podcast container holding AAC-encoded audio along with chapter markers, bookmarks, and metadata. FFmpeg reads the MPEG-4 container structure to extract all streams and timing data before conversion begins.
-c:a libvorbis Sets the audio encoder to libvorbis, the reference implementation of the Vorbis codec, which produces OGG-compatible audio. This triggers a full re-encode of the AAC audio from the M4B into the royalty-free Vorbis format — unlike remuxing, every audio sample is decoded and re-compressed.
-q:a 4 Sets the Vorbis variable bitrate quality on a scale from 0 to 10, with 4 targeting approximately 128kbps — well-suited for audiobook and podcast speech content. Unlike M4B's -b:a bitrate parameter, Vorbis uses this quality scale to allocate bits dynamically, so quieter passages use fewer bits than complex audio sections.
output.ogg Defines the output filename with the .ogg extension, which tells FFmpeg to wrap the encoded Vorbis audio stream in an OGG container. The OGG container carries the Vorbis audio along with any chapter metadata and Vorbis Comment tags mapped from the original M4B.

Common Use Cases

  • Making an audiobook purchased in M4B format playable on Linux media players like VLC or Rhythmbox that prefer open codec formats
  • Converting M4B podcast episodes to OGG for upload to platforms or RSS feeds that accept Vorbis audio without requiring proprietary Apple-format files
  • Stripping Apple ecosystem dependencies from an audiobook collection so files play natively on Android devices using apps like AntennaPod or Voice audiobook player
  • Archiving audiobooks in a patent-free, open format as part of a long-term digital library strategy where codec licensing is a concern
  • Preparing audiobook audio for embedding in web applications or games using the HTML5 Audio API, where OGG Vorbis has broad browser support as a royalty-free alternative to AAC
  • Converting M4B files for use on dedicated e-readers or media players that support OGG but not MPEG-4 audio containers

Frequently Asked Questions

The OGG container does support chapter metadata, and FFmpeg will attempt to carry chapter timing data from the M4B into the OGG output. However, support for reading OGG chapters depends heavily on your playback software — not all OGG-compatible players implement chapter navigation. Apple's bookmarking feature (which saves your listening position) is M4B-specific and will not be preserved in the OGG file.
Because both AAC and Vorbis are lossy codecs, this conversion involves decoding the AAC audio to raw PCM and then re-encoding it as Vorbis, which introduces a second generation of lossy compression artifacts. The default -q:a 4 setting produces Vorbis audio roughly equivalent to 128kbps, which is typically transparent for spoken-word audiobooks and podcasts. For music-heavy audiobooks or maximum quality, increase -q:a to 6 or higher.
Replace the -q:a 4 value with any integer from 0 (lowest quality, smallest file) to 10 (highest quality, largest file). For audiobooks and podcasts, -q:a 3 or 4 is generally sufficient since the content is speech. If you need smaller files for streaming or storage-constrained devices, -q:a 2 is still quite acceptable for voice audio. The full adjusted command would look like: ffmpeg -i input.m4b -c:a libvorbis -q:a 6 output.ogg
Yes. On Linux or macOS, you can loop over all M4B files in a directory with: for f in *.m4b; do ffmpeg -i "$f" -c:a libvorbis -q:a 4 "${f%.m4b}.ogg"; done. On Windows Command Prompt, use: for %f in (*.m4b) do ffmpeg -i "%f" -c:a libvorbis -q:a 4 "%~nf.ogg". The browser-based tool on this page processes one file at a time, so the command-line approach is recommended for large collections.
File size depends on the bitrate of the original M4B's AAC stream compared to the output Vorbis quality setting. M4B audiobooks often use low AAC bitrates (64–96kbps) to keep files small. The default -q:a 4 Vorbis setting targets roughly 128kbps, so if your source was encoded at a lower bitrate, the OGG file may actually be larger. You can lower the -q:a value (try 2 or 3) to produce smaller output files more comparable to the source.
No. Apple's native apps — including the Books app, Podcasts app, and iTunes — do not support OGG Vorbis playback. Converting from M4B to OGG is intended for open-platform ecosystems such as Android, Linux, or web-based players. If you need a format compatible with Apple devices, consider converting to MP3 or keeping the M4B format.

Technical Notes

The M4B-to-OGG conversion is always a full transcode — there is no shortcut remux path because AAC (used in M4B) and Vorbis (the default OGG audio codec) are entirely different encoding algorithms. The Vorbis encoder uses a quality-based VBR scheme where -q:a values map approximately as follows: q2 ≈ 80kbps, q4 ≈ 128kbps, q6 ≈ 192kbps, q10 ≈ 500kbps. For spoken-word content like audiobooks, q3 or q4 is indistinguishable from higher settings in listening tests. Metadata such as title, artist, and album tags are mapped from the M4B's MP4 atoms to OGG's Vorbis Comment format by FFmpeg, though some M4B-specific tags (like the Apple chapter image artwork embedded per-chapter) may not transfer cleanly. The OGG container does not support DRM, so M4B files protected by Apple's FairPlay DRM cannot be converted — only DRM-free M4B files (such as those from DRM-free audiobook stores or self-recorded content) will work with this tool. Files processed here stay entirely in your browser memory via FFmpeg.wasm; for files over 1GB, the desktop FFmpeg command shown on this page is the recommended approach.

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